It might be trying to detect dial tone, then hanging up and trying again after a second or so - the click would be the mechanical relay you see in the schematic

It might be trying to detect dial tone, then hanging up and trying again after a second or so - the click would be the mechanical relay you see in the schematic. (note that standard phone lines don't send dial tone until they detect an off-hook condition, i.e. current flowing down the line. Even then, older exchanges had a limited number of "dialers", and wouldn't send dial tone until one had been connected to the line)